Rogue Planet ‘Nomads’ May Outnumber Stars In Milky Way

Our Milky Way galaxy may be teeming with rogue planets that ramble through space instead of being locked in orbit around a star, a new study suggests.

These “nomad planets” could be surprisingly common in our bustling galaxy, according to researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the SLAC National Accelerator Laboratory. The study predicts that there may be 100,000 times more of these wandering, homeless planets than stars in the Milky Way.

If this is the case, these intriguing cosmic bodies would belong to a whole new class of alien worlds, shaking up existing theories of planet formation. These free-flying planets may also raise new and tantalizing questions in the search for life beyond Earth.

“If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist,” study leader Louis Strigari said in a statement.

And while nomad planets cannot benefit from the heat given off from their parent stars, these worlds could generate heat from tectonic activity or internal radioactive decay, the researchers said.

For now, characteristics of these foreign objects are still unknown; they could be icy bodies, similar to other objects found in the outer solar system, rocky like asteroids, or gas giants similar to the most massive planets in our solar system.

Over the past several decades, astronomers have keenly hunted for planets outside our solar system. So far, the search has turned up more than 700 of these exoplanets. Almost all of these newfound worlds orbit stars, but last year, scientists found about a dozen planets with no discernible host star.

The researchers used a technique called gravitational microlensing to detect these homeless planets. This method examines the effects of a massive object passing in front of a star.

From Earth, the nearby object bends and magnifies the light from the distant star like a lens, making the faraway star’s light appear to brighten and fade over time. The resulting “light curve” helps astronomers distinguish characteristics of the foreground object.